The present invention relates to methods and apparatus for storing data, including error compensation data, locally on probes for use with a cable tester so as to enable accurate identification, maintenance and error correction of data obtained via the probe.
The challenge to manufacturers of cables and connectors has been to improve the performance of their products to provide a better transmission environment for ever-higher data transmission rates. At present, the structured cabling industry is transitioning from category 5 products and standards to category 6 products and standards. This transition will continue for some time as product innovation continues and as standards documents continue to evolve. Cable manufacturers employ a wide variety of materials and construction techniques to improve the performance of cable to meet the new standards. Recent emphasis has been on reducing process variations and optimizing cable construction in an effort to reduce crosstalk between pairs and reflections within pairs.
To ensure that structured cabling systems provide adequate performance to support the utilized application interfaces, cabling standards committees have developed quality control specifications for the installation of new cabling. Cable testers provide a convenient and reliable means of certifying new installations for compliance with structured cabling standards. Standards for structured twisted pair cabling require that both ends of each cabling run be tested in order to find the worst case performance condition. For this reason, all certification testing requires a two-part test set, consisting of a main unit and a remote unit. One unit tests the cabling run from the telecommunications closet end and the other unit tests the cabling run from the telecommunications outlet end at the user location.
Certification testing is highly automated. Typically, an automated function coordinates a series of measurements between the main unit and the remote unit and subsequently analyzes the resulting data to determine if the cabling run passes or fails the required standards. Two key criteria apply in determining the extent of a test for any particular cabling run:
1) Whether the user patch cords are included in the cabling run during the test (i.e., xe2x80x9cLinkxe2x80x9d or xe2x80x9cChannelxe2x80x9d test configuration)
2) What standard document and which performance level the user wishes to test the cabling to (i.e., for what xe2x80x9ccategoryxe2x80x9d is the user seeking certification)
FIG. 1 is a diagram of a known testing circuit 100 in a link test configuration. The testing circuit 100 tests a cable 110 which provides a communication path between a telecommunications closet end 112 and a telecommunications outlet end 114. The configuration of the testing circuit 100 shown in FIG. 1 is a xe2x80x9clink configurationxe2x80x9d intended for use in facilities still in the construction stage. The link configuration does not include user patch cords at either end of the cabling run as these cords are often not installed until after the facility is occupied. Because the link configuration does not include the two additional connections which would be added when the patch cords are connected, performance standards are more stringent for cabling tested using the link configuration.
A main unit 116 and a remote unit 118 attach to the link under test, the cable 110, via special link test probes 120a and 120b respectively. The link test probes 120a and 120b are provided with interfaces 122a and 122b for connection to the main unit 116 and the remote unit 118 respectively. The link test probes 120a and 120b are typically terminated at their opposite ends with male modular-8 plugs 124a and 124b, respectively, for connection to the telecommunications closet end 112 and the telecommunications outlet end 114, respectively.
FIG. 2 is a diagram of a known testing circuit 200 in a channel test configuration. The testing circuit 200, like the testing circuit 100, tests a cable 110 which provides a communication path between a telecommunications closet end 112 and a telecommunications outlet end 114. In addition, the test produced by the testing circuit 200 includes the effect of user patch cords 220a and 220b, thereby providing a comprehensive end-to-end cabling performance certification. The patch cords are typically created as the network is going live, and, as such, a channel test is typically performed after the facilities have been constructed, either as a final test prior to going live, or to diagnose subsequent problems. The pass/fail limits applied when testing with the channel configuration will typically be less stringent than for the link configuration
A main unit 116 and a remote unit 118 attach to the link under test, the cable 110 and user patch cords 220a and 220b, via special channel probes 222a and 222b respectively. The channel probes 220a and 220b are provided with interfaces for connection to the main unit 116 and the remote unit 118, respectively. On the opposite ends, the channel probes 222a and 222b are typically terminated with female modular-8 plugs 122a and 122b, respectively, for connection to the user leads 220a and 220b, respectively.
One problem encountered when testing cables, and in particular category 6 cables, is correctly matching the test units (the main unit 116 and the remote unit 118) to the link under test. This is not as simple as picking between a link and a channel adapter, but rather a broad range of choices faces the user. There exist a multitude of different link probes, along with an equal multitude of channel probes. Not only do users have to select between link and channel probes, but they must also match the probe to the manufacture of the network. This choice is made more difficult by the physical similarities of the probes used, while the difference between a channel probe and a link probe may be self-evident, each of the various probes with the channel probe family or link probe family pretty much look exactly the same. Each probe starts with a tester unit interface and ends in a modular-8 connector. As will be discussed below, the choice of which probe to utilize is critical to obtaining accurate testing results.
The modular-8 connector (also known as the RJ-45), was originally designed for telephone and low rate (under 1 Mbps) data applications. Consequently, the mechanical arrangement of signal contacts is not optimized to address the crosstalk and reflection problems that appear at high data rates (over 100 Mbps). Many ingenious designs have been utilized to compensate for the inherently poor performance that results from the modular-8 contact geometry. In the previous generation of connector designs (category 5), most manufacturers used signal compensation in just the jack (female connector), leaving the plug (male connector) uncompensated. To achieve the higher performance levels required for category 6 and maintain backward compatibility with the modular-8 signal contact geometry, most connector manufacturers place compensation into both the plug and jack. It is important that the compensation techniques used in each plug and jack of the network be compatible. The interaction between incompatible plug and jack compensation designs produces worse performance than previous level 5 connectors. This is one reason why certification is so important
Unfortunately, no standards currently exit for the physical and logical construction of category 6 connectors and associated compensation techniques. In fact, cables and connectors from different manufactures are often incompatible with each other. Accordingly, to construct a category 6 network, users have to make sure that they match the brand and type of category 6 plugs and jacks in order to achieve optimum system performance.
The requirement to match category 6 plugs and jacks also applies to the link probes and channel adapters used for cable certification testing. When testing category 6 or class E cabling runs, it is particularly important to use the test probes which are specifically designed to match the test configuration, performance category and manufacturer corresponding to the cabling to be tested. Failure to use the correctly matched probes will yield inaccurate measurements. For this reason, a cable tester must utilize a range line of vendor-specific category 6 link and channel adapters constructed with plugs and jacks from each of the major connector manufacturers. As noted above, because the cables and terminators all look the same, identification of the correct probe becomes a problem.
Another problem related to the use of modular 8 connectors is that after repeated insertion and extraction, they tend to wear out. This problem is more pronounced with the connectors on the probe because they see a tremendous amount of use. Worn out probe connectors affect the cable tester""s ability to obtain an adequate electrical connection, thereby skewing test results producing erroneous certification data. Currently, the only way to check for worn connectors on a probe is to inspect the connectors visually and periodically bench test the probe to determine if the probes associated error factors lie within specification. As with many maintenance procedures, this such checks are rarely performed, resulting in unnecessary frustration and aggravation.
Yet another problem with current cable testers and testing methods is that they require constant calibration to provide accurate testing results. FIG. 3 is a diagram of a known cable tester calibration circuit. To ensure completely accurate testing with the main unit 116 and the remote unit 118, it is necessary to compensate for the effects of a channel probe 312 and/or a link probe (not shown). To perform calibration, a cable, such as a link cable 310, with known error values (obtained via bench tested) is used to connect the channel probe 312 (connected to the main unit 116) to the remote unit 118. The main unit 116 and the remote unit 118 run a calibration routine to determine the error terms associated with the cable tester. Then, prior to starting a calibration procedure, error terms associated with the probes being used (determined by bench measurement) must be manually entered into the main unit 116. The calibration procedure should be repeated frequently while the entering of error terms associated with the probes must be performed every time a new probe is use. In practice, this has been a problem, operators tend to be very busy and forget to regularly perform the calibration routine and, more importantly, fail to enter the probe""s error terms creating erroneous certification data.
Accordingly, the present inventors have recognized a need for probes for cable testers that can assist the operator with configuration issues and track usage thereof.
The present invention provides test probes having a memory for storing configuration data, including error correction values, and a counter that logs a number of tests performed by the probe. As a result, a cable tester in accordance with the present invention can warn the user, prior to attempting a test procedure, if an attached test probe is inappropriate for selected test limits, either because it is the wrong probe or because of wear and tear. This helps the operator avoid wasting time testing with the wrong probe/settings configuration. Once the probe had been correctly selected, the stored error correction factors allow the cable tester to compensate therefore reducing the need for repeated calibration procedures.